diff --git a/src/github.com/matrix-org/dendrite/clientapi/auth/auth.go b/src/github.com/matrix-org/dendrite/clientapi/auth/auth.go
index 927e294c5..cb809dcd3 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/auth/auth.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/auth/auth.go
@@ -6,17 +6,24 @@ import (
 	"strings"
 
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/util"
 )
 
 // VerifyAccessToken verifies that an access token was supplied in the given HTTP request
-// and returns the user ID it corresponds to. Returns an error if there is no access token
-// or the token is invalid.
-func VerifyAccessToken(req *http.Request) (userID string, err error) {
-	_, tokenErr := extractAccessToken(req)
+// and returns the user ID it corresponds to. Returns err if there was a fatal problem checking
+// the token. Returns resErr (an error response which can be sent to the client) if the token is invalid.
+func VerifyAccessToken(req *http.Request) (userID string, resErr *util.JSONResponse, err error) {
+	token, tokenErr := extractAccessToken(req)
 	if tokenErr != nil {
-		err = jsonerror.MissingToken(tokenErr.Error())
+		resErr = &util.JSONResponse{
+			Code: 401,
+			JSON: jsonerror.MissingToken(tokenErr.Error()),
+		}
 		return
 	}
+	if token == "fail" {
+		err = fmt.Errorf("Fatal error")
+	}
 	// TODO: Check the token against the database
 	return
 }
diff --git a/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go b/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go
index a0111197c..ea64896db 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go
@@ -1,6 +1,9 @@
 package jsonerror
 
-import "fmt"
+import (
+	"fmt"
+	"github.com/matrix-org/util"
+)
 
 // MatrixError represents the "standard error response" in Matrix.
 // http://matrix.org/docs/spec/client_server/r0.2.0.html#api-standards
@@ -13,6 +16,20 @@ func (e *MatrixError) Error() string {
 	return fmt.Sprintf("%s: %s", e.ErrCode, e.Err)
 }
 
+// InternalServerError returns a 500 Internal Server Error in a matrix-compliant
+// format.
+func InternalServerError() util.JSONResponse {
+	return util.JSONResponse{
+		Code: 500,
+		JSON: Unknown("Internal Server Error"),
+	}
+}
+
+// Unknown is an unexpected error
+func Unknown(msg string) *MatrixError {
+	return &MatrixError{"M_UNKNOWN", msg}
+}
+
 // Forbidden is an error when the client tries to access a resource
 // they are not allowed to access.
 func Forbidden(msg string) *MatrixError {
diff --git a/src/github.com/matrix-org/dendrite/clientapi/readers/sync.go b/src/github.com/matrix-org/dendrite/clientapi/readers/sync.go
index 8db717103..05def8148 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/readers/sync.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/readers/sync.go
@@ -4,18 +4,20 @@ import (
 	"net/http"
 
 	"github.com/matrix-org/dendrite/clientapi/auth"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/util"
 )
 
 // Sync implements /sync
 func Sync(req *http.Request) util.JSONResponse {
 	logger := util.GetLogger(req.Context())
-	userID, err := auth.VerifyAccessToken(req)
+	userID, resErr, err := auth.VerifyAccessToken(req)
 	if err != nil {
-		return util.JSONResponse{
-			Code: 403,
-			JSON: err,
-		}
+		logger.WithError(err).Error("Failed to verify access token")
+		return jsonerror.InternalServerError()
+	}
+	if resErr != nil {
+		return *resErr
 	}
 
 	logger.WithField("userID", userID).Info("Doing stuff...")
diff --git a/src/github.com/matrix-org/dendrite/clientapi/writers/sendmessage.go b/src/github.com/matrix-org/dendrite/clientapi/writers/sendmessage.go
index d6713b1af..4b8ad9052 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/writers/sendmessage.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/writers/sendmessage.go
@@ -5,18 +5,20 @@ import (
 
 	log "github.com/Sirupsen/logrus"
 	"github.com/matrix-org/dendrite/clientapi/auth"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/util"
 )
 
 // SendMessage implements /rooms/{roomID}/send/{eventType}
 func SendMessage(req *http.Request, roomID, eventType string) util.JSONResponse {
 	logger := util.GetLogger(req.Context())
-	userID, err := auth.VerifyAccessToken(req)
+	userID, resErr, err := auth.VerifyAccessToken(req)
 	if err != nil {
-		return util.JSONResponse{
-			Code: 403,
-			JSON: err,
-		}
+		logger.WithError(err).Error("Failed to verify access token")
+		return jsonerror.InternalServerError()
+	}
+	if resErr != nil {
+		return *resErr
 	}
 	logger.WithFields(log.Fields{
 		"roomID":    roomID,